Emboldened by a belief that their political fortunes are on the rise, conservative activists descended Thursday on the capital city they love to hate, seeking to stoke what they consider a grass-roots uprising against President Obama and Democrats in Congress.

The annual Conservative Political Action Conference was once a venue for the right fringe of the Republican Party, but in recent years it has drawn more mainstream party figures and now provides a stage for presidential aspirants to prove their conservative credentials.

This year's CPAC, which began Thursday and will run through Saturday, had a festival atmosphere, as thousands of jubilant activists turned the Marriott Wardman Park ballroom into a hive of old-guard conservatives and Don't Tread on Me "tea partiers" hungry for new leaders and messages that can carry the GOP out of the political wilderness.

It was, in the words of one speaker, "our Woodstock."

Featured speakers in the opening session included former Massachusetts governor Mitt Romney, who sought to turn the page on his 2008 presidential campaign by casting himself as a populist and every bit the conservative standard-bearer. He defended the policies of former president George W. Bush and his party's lockstep opposition to Obama's agenda, saying that Obama had "failed" and that the Democratic majority in Congress would "soon be out the door."

"If these liberal neo-monarchists succeed, they will kill the very spirit that has built the nation -- the innovating, inventing, creating, independent current that runs from coast to coast," Romney said. Pounding on the lectern as the audience leapt up, he declared: "And we won't let 'em do it."

The attendees stomped and screamed at the appearance of the surprise guest who introduced Romney: Scott Brown. "I'm the newly elected Republican senator from Massachusetts," Brown said. "Let me just say that one more time. I am the Republican senator from Massachusetts."

Former vice president Richard B. Cheney also made an unscheduled appearance, bounding out from behind the dark curtain with his daughter Liz. He received a hero's welcome, to cries of "Run, Dick, run!"

"Knock it off," Cheney quipped. "A welcome like that's almost enough to make me want to run for office, but I'm not gonna do it."

Since the days of President Richard M. Nixon, CPAC has served as an annual gathering of conservative thinkers. But now it is an important venue for any ambitious Republican, and this year's agenda features potential presidential hopefuls. In addition to Romney, Minnesota Gov. Tim Pawlenty and Rep. Mike Pence (Ind.) will speak Friday, while former senator Rick Santorum (Pa.) and former House speaker Newt Gingrich (Ga.) will speak Saturday, before the results of a presidential straw poll are released. Former Alaska governor Sarah Palin is not expected to attend.

The gathering continues to draw its share of firebrands. Dana Loesch, a St. Louis radio host and a tea party leader there, challenged conservatives to organize in unexpected ways -- over burgers and brews at bars where liberals congregate or by starting "flash mobs." Longtime National Rifle Association leader Wayne LaPierre gave an impassioned tribute to Charlton Heston, the late actor and NRA president.

And at a time of strife within the Republican Party, which lacks a clear national leader and is struggling to unite behind a common agenda as the November midterm elections approach, one theme emerged in each speech Thursday: Attack Obama.